SQL server 去掉反复字段

SQL server 去掉重复字段
现在有这么一个游戏角色表，里面保存的字段有UserID、ActorID、ActorLevel、Experience、WriteTime，
要求是每个UserID下只保留一个ActorID，且这个ActorID的ActorLevel是最大的，如果ActorLevel相同，则保留Experience最高的，否则保留WriteTime最早的。
我是这么写的：
DELETE dbo.GameActor FROM dbo.GameActor a
WHERE (
  SELECT COUNT(ActorLevel) 
  FROM dbo.GameActor
  WHERE （UserID=a.UserID AND ActorLevel>a.ActorLevel） OR (UserID=a.UserID AND ActorLevel=a.ActorLevel 
  AND Experience>a.Experience) OR (UserID=a.UserID AND ActorLevel=a.ActorLevel 
  AND Experience=a.Experience AND WriteTime>a.WriteTime)
  )
  )>1
这个的执行效率太低 谁能帮我改进下？ 谢谢

[解决办法]

SQL code

DELETE dbo.GameActor FROM dbo.GameActor aWHERE EXISTS(  SELECT 1   FROM dbo.GameActor  WHERE （UserID=a.UserID AND ActorLevel>a.ActorLevel） OR (UserID=a.UserID AND ActorLevel=a.ActorLevel    AND Experience>a.Experience) OR (UserID=a.UserID AND ActorLevel=a.ActorLevel    AND Experience=a.Experience AND WriteTime>a.WriteTime)  )
[解决办法]
SQL code
-->tryDELETE dbo.GameActor FROM dbo.GameActor aWHERE ( SELECT COUNT(ActorLevel)          FROM dbo.GameActor        WHERE UserID=a.UserID AND ((ActorLevel>a.ActorLevel)                                 or (ActorLevel=a.ActorLevel AND Experience>a.Experience))         --OR (UserID=a.UserID AND ActorLevel=a.ActorLevel AND Experience=a.Experience AND WriteTime>a.WriteTime)      )>1